In gear transmission apparatus, a driven wheel is usually connected with an output shaft, and a driving wheel meshes with the driven wheel directly or via an idle wheel, thereby changing a rotating speed, a torque, or a rotating direction of the output shaft relative to the driving wheel. In conventional gear transmission apparatus, when the rotating direction of the driving wheel changes, a direction of the output shaft changes correspondingly. In use of such gear transmission apparatus, a driving device for the driving wheel is required to have a determined rotating direction, and the rotating direction should be determined at the time the driving device is assembled. Once the driving device rotates reversely, the gear transmission apparatus may be damaged. In addition, sometimes when the driving device rotates reversely, the driving device may perform idle work, which decreases energy utilization efficiency.